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Oslonci i potresno opterećenje za projektiranje konstrukcija obično su matematički izvodi podataka dobivenih iz profila tala sa slobodnom površinom. Ovo istraživanje je vođeno pretpostavkom da pritisak od konstrukcije na tlo može promijeniti rezonantna svojstva tla i tako preusmjeriti projektiranje konstrukcija. Istraživanje je provedeno na setu od 10 stvarnih profila tla; na 21 studiji slučaja i koristeći dvije metode za korekciju profila brzina posmičnih valova s ciljem uključivanja kontaktnog pritiska. Analitički dobiveni rezultati su uspoređeni s pandanima dobivenim iz eksperimenta provedenog u centrifugi., The supports and seismic actions for structural design are usually mathematical derivatives of the data collected from soil profiles with free-field conditions. This study is based on the premise that the pressure exerted by the structure onto the soil can change resonant properties of soil and thus redirect structural design. The research was conducted on a set of 10 real soil profiles, and involves 21 case studies and the use of two methods for correction of shear wave velocity profiles in order to include contact pressure. Analytically obtained results are compared with the corresponding results obtained by means of a centrifuge experiment, Unterstützung und Erbebenbelastung für die Projektierung von Konstruktionen sind in der Regel mathematische Ableitungen von Daten, die aus den Bodenprofilen mit freien Oberflächen erhalten werden. Diese Untersuchung basiert auf der Annahme, dass der Druck der Konstruktion auf den Boden die Resonanzeigenschaften des Bodens verändern und somit die Projektierung der Konstruktionen umlenken kann. Die Untersuchung wurde an einem Set von 10 realen Bodenprofilen durchgeführt; anhand von 21 Fallstudien und zwei Methoden werden Scherwellengeschwindigkeitsprofile mit dem Ziel korrigiert, den Anpressdruck zu berücksichtigen. Die analytisch erhaltenen Ergebnisse wurden mit den aus dem Zentrifugenexperiment erhaltenen Gegenstücken verglichen.

A frequent dilemma in seismic design of buildings founded on soft soils is how to include soil compliance in numerical models. Although various international building codes propose methods for soil-structure interaction (SSI) modeling, common engineering practice is to model and design buildings as being fixed into the ground. Different codes propose different methods for including SSI effects into the seismic design of buildings and they are mostly based upon impedance functions. Impedance functions serve as an efficient replacement for demanding soil models under buildings. Since codes from around the world use different expressions and different models for soil modeling, numerical research and parametric study on a scaled model of a two- dimensional frame is conducted in order to determine the efficiency of each tested method. To verify the efficiency of the tested methods, a numerical model was developed in which a frame model was subjected to nonlin-ear static pushover analysis. Results obtained from the numerical analysis are compared to the results obtained on the experimentally tested frame at the Laboratory for experimental mechanics at the Faculty of Civil Engineering and Architecture Osijek.

Reinforced concrete buildings represent the largest share of the world’s building’s stock. Although such buildings are usually designed to endure extreme loadings, their structural elements can deform and manifest cracks. Large cracks can point out problems related to structural health. For instance, hairline cracks can cause reinforcement corrosion. In addition, many existing cracks can be hidden by façade or can be difficult to determine due to inaccessibility to the structural element. Thus, many cracks cannot be easily detected by simple visual inspection of the building. Following the idea on how simple burglar alarm circuits and home security systems work we have proposed a sensor for monitoring occurrence of cracks in reinforced concrete buildings. The detector was experimentally tested in a centrifuge using a small-scale mock-up representing a real reinforced concrete system. This paper, inter alia, demonstrates scaling rules for centrifuges and how those rules are applied to a model used to mimic behaviour of real large scale reinforced concrete structures. Different small scale models comprising beams and slabs are made of gypsum mixtures. All the models were tested in the laboratories of the Faculty of Civil Engineering Osijek using a 0, 40 m in radius centrifuge. The off-the shelf detector showed good potential in discovering crack occurrence on structural parts in buildings.

European norms propose several different approaches for seismic design of buildings. One of the approaches considered fast, accurate but simple as well is N2 method. Although N2 method is commonly used by academic community, it still consists limitations regarding soil- structure interaction. When building is designed it is considered fixed into the ground which does not accurately present buildings on shallow foundations founded on soft soil. When determining dynamic properties of buildings changes (longer fundamental period of oscillations, increased damping) are evident when soft soil under the structure is included, yet, there are no proposed method for this problem in the European norms. Within the experimental research underway in Osijek soil structure interaction effects are observed. First part of the experimental research is presented in this paper which includes determination of model and its behavior when fixed into the ground. Also, further research ideas are presented.

N2 je brza nelinearna statička metoda za projektiranje zgrada otpornih na potres. Rad predstavlja značajke i ograničenja metode, njezin razvoj te mogućnosti primjene na različitim tipovima zgrada. Istaknute su razlike između klasične N2 metode i njezinih proširenja. Također, dana je usporedba N2 metode i sličnih proračunskih pristupa. Ustanovljeno je da se rezultati dobiveni proračunima uz primjenu N2 metode dobro slažu s rezultatima dobivenim uz primjenu znatno složenijih metoda. Na kraju su dane smjernice za daljnje istraživanje., The N2 method is a fast nonlinear static method for the seismic design of buildings. This paper presents main properties and limitations of the method, its development over time, and possibilities of its application for different types of buildings. Differences between the traditional N2 method and its extensions are highlighted. Comparison of the N2 method with similar design approaches is also provided. The results obtained by calculations based on the N2 method are found to be in good agreement with the results obtained by much more complex methods. Guidelines for further research are given in the final part of the paper., N2 ist eine schnelle nicht lineare statische Methode für die Planung von erbebensicheren Gebäuden. Die Abhandlung stellt die Merkmale und die Grenzen der Methode, deren Entwicklung sowie die Möglichkeiten der Anwendung an verschiedenen Gebäudetypen vor. Hervorgehoben werden die Unterschiede zwischen der klassischen N2 Methode und deren Erweiterungen. Des Weiteren wird ein Vergleich der N2 Methode und ähnlicher Berechnungsansätze dargelegt. Es wurde festgestellt, dass die Ergebnisse, die durch die Berechnung durch Anwendung der N2 Methode erhalten wurden, gut zu den Ergebnissen passen, die man durch die Anwendung wesentlich komplexerer Methoden erhalten hat. Am Ende werden Richtlinien für weitere Untersuchungen gegeben.

The very beginnings of the N2 method started in late 1980s. Since then the method has been developing by many researchers. The N2 method is a nonlinear static method implemented in European norms and it is considered as a useful tool in seismic design of buildings. In this paper, the N2 method results are compared to the results obtained from the Blind Test Challenge conducted in Portugal in 2012. Within the challenge a 3D reinforced concrete frame model was experimentally tested using bi-directional shaking table. Data comprising displacement time history records was available to the authors and used in this research. The N2 method was applied to the concrete 3D frame model. Using the method target displacement was determined and compared to displacements recorded during the experiment.

U radu je promatrana armiranobetonska konstrukcija eksperimentalno ispitana na potresnome stolu. Fizički je model konstrukcije ispitan u četiri faze, pri čemu je svaka faza uključivala potres snažnijega intenziteta. To je omogućilo istraživanje utjecaja oštećenja konstrukcije na njezina dinamička svojstva: prigušenje i osnovni period osciliranja. Za promatranu je konstrukciju napravljena procjena prigušenja i osnovnoga perioda osciliranja nakon svake završene faze ispitivanja primjenom vremenskih zapisa pomaka dostupnih autorima. Rezultati dobiveni na stvarnoj konstrukciji uspoređeni su s preporučenim vrijednostima prigušenja te proračunanim vrijednostima osnovnoga perioda osciliranja uz primjenu analitičkih izraza iz dostupne literature. Osim toga, u radu je prikazan i jednostavan način filtriranja i zaglađivanja vremenskih zapisa koji sadrži visoko frekvencijski šum., This paper observes reinforced concrete structure experimentally tested on a shaking table. The physical model of the structure was tested in four phases where each phase involved shaking of higher intensity. This allowed study of the influence of structural damage on its dynamic properties. For the observed structure an estimation of the damping and the natural period of oscillation was made after each completed phase of the test using displacement time history records available to the authors. The results obtained from the real structure were compared with the recommended values of damping and calculated values of the fundamental period of oscillation using analytical expressions provided in available literature. Besides that, the paper shows simple way of filtering and smoothing of time histories that comprises high frequency noise.

U južnoj Europi postoji značajna povijest seizmičke aktivnosti koja je kao posljedicu imala značajan utjecaj na stanovništvo i ekonomiju cijele države. Kako bi se uočilo na posljedicama potresa koji su pogodili Jugoslaviju i greškama u projektiranju građevina, treba sagledati povijest seizmičke aktivnosti ovoga područja. Odabirom reprezentativne građevine južne Europe započeti će se proces ocjene modela seizmičkog ponašanja zidanih zgrada koji se nastavlja modeliranjem te provođenjem pushover analize na dva različita modela u dva različita kompjuterska programa. Dobiveni rezultati prikazat će ponašanje modela na horizontalno opterećenje te će dobiveni rezultati biti međusobno uspoređeni., Southern Europe had a few earthquakes that caused catastrophes in the past with great consequences on population. Trying to learn from this catastrophes and building mistakes, some of the most impacting earthquakes will be taken into consideration. From this point of view it is necessary to compose a building stock for this ExYugoslavian countries and choose one which will be representative and used for modelling. Pushover analysis will be computed on two different models with two different softwares and the results given by analysis will be mutually compared. Results should show behaviour of the masonry buildings under the horizontal load .

Design of economically justified and earthquake resistant structures is multidisciplinary and challenging task. Due to complexity in modeling and high computational costs it is often the case that soil – a vast medium that gives support to structures but also that transmits devastating vibrations – is neglected from analyses or is simply modeled using simplified discrete spring. The field of dynamic soil-structure interaction (SSI) is still vastly unexplored, while the root of its issues mostly lies in the fact that soil-structure systems – due to their pronounced nonlinearity and big appetite for parameters and variables – are still computationally very demanding. This is particularly a problem for engineering practice which looks for simple – yet safe and well tested – methods for analyses, as the deadlines are often very tight. The European N2 method is coded performance-based design method for analysis of earthquake resistant structures. This method is simple and offers good results for structural design but, due to its novelty, engineering practice still does not recognize it. On the other end, this method is nowadays very much discussed in European high-quality journals and it is included in earthquake engineering lectures provided to graduate students. Nevertheless, this method still looks for testing and validation against experimental results, but also for improvements regarding including the SSI effects. Existing experiments can provide good insight on seismic behavior of real structures. Yet, these experiments have some shortcomings and disadvantages that cannot support improvements of the N2 method: (i) structures cannot undergo plastic deformations, which is an essential structural behavior that governs the N2 method, (ii) contact pressure between the soil and foundation model is not realistic and (iii) it is not always easy to instrument small-scale models – clearly, only large-scale models can provide the most reliable and trustworthy results to support better understanding of behavior of structures. A project recently started at the Faculty of Civil Engineering Osijek has an aim to eliminate the above mentioned shortcomings and to improve the N2 method. A set of large-scale soil-structure models with possibility of plastification of structural elements and well simulated bearing pressures will be conducted. The final outcome of the improved method will be safer urban environment with modern structures that will resist strong ground shaking.

Since 2013, the Association of Students of the Faculty of Civil Engineering Osijek (s-gfos) has been organizing the International Summer Conference of Civil Engineering Students. Proceedings are intended for the popularization of science and the promotion of inter-faculty and inter-university cooperation with civil engineering faculties of other European countries. Apart from Croatia, students from different European countries, including the USA, participate in the workshop every year.

Od 2013. godine Udruga studenata građevinskog fakulteta Osijek (s-gfos) organizira International Summer Conference of Civil Engineering Students. Zbornik je namijenjen popularizaciji znanosti i promidžbi međufakultetske i među- sveučilišne suradnje s građevinskim fakultetima drugih europskih zemalja. Osim iz Hrvatske, na radionici svake godine sudjeluju studenti iz različitih europskih zemalja.